Re: [Boost-users] metafunction question

Subject: Re: [Boost-users] metafunction question
From: strasser_at_[hidden]
Date: 2010-05-11 15:49:02

Zitat von John Dlugosz <JDlugosz_at_[hidden]>:

> A co-worker mentioned an interesting issue.  I thought some  
> metaprogramming, or at least more advanced insight into STL, might  
> apply here.
>
> Consider a class derived from an STL collection.  It features a  
> special find(x) function that works with his search criteria.  It  
> returns an iterator into the collection.  There are two forms needed:
> 	iterator find(x);
> 	const_iterator find(x) const;
> and the annoying part is that they contain exactly the same code.   
> The implementation uses the inherited iterators and collection  
> features to do the finding.
>
> The larger question is, is there a better way to approach that?
>
> The immediate question is, my thought of using a template helper  
> requires the return type to be determined based on the constness of  
> the incoming parameter for the collection type.

the return type cannot be parametrized based on the const-ness of  
"this". but parametrizing _functions_ based on constness rarely makes  
sense anyway, the best aproach imho is to keep the overloads but let  
them only handle the const/non-const specific stuff and forward the  
rest.
in your example:

private:
   node_ptr find_node(x) const;
public:
   iterator find(x){ return iterator(find_node(x)); }
   const_iterator find(x) const{ return const_iterator(find_node(x)); }